Hydraulic torque converters, devices used to change the ratio of torque to speed between the input and output shafts of the converter, revolutionized the automotive and marine propulsion industries by providing hydraulic means to transfer energy from an engine to a drive mechanism, e.g., drive shaft or automatic transmission, while smoothing out engine power pulses. A torque converter, arranged between the engine and the transmission, includes three primary components, an impeller, sometimes referred to as a pump, directly connected to the converter's cover and thereby the engine's crankshaft; a turbine, similar in structure to the impeller, however the turbine is connected to the input shaft of the transmission; and, a stator, located between the impeller and turbine, which redirects the flow of hydraulic fluid exiting from the turbine thereby providing additional rotational force to the pump.
Although coupling the impeller to the engine, at first glance, may appear trivial, the means by which the coupling is accomplished can radically effect the performance and efficiency of the engine and torque converter, e.g., resulting in varying horsepower at the wheels. The push for increased fuel economy/gas mileage and decreased manufacturing costs encouraged the development of torque converter drive plates having various configurations. For example, in one design, tabs or extensions are forged or welded on a torque converter cover, thereby providing an integral means of coupling a converter to an engine. Although this design may be quite simple, it does however introduce a significant amount of dense material to the torque converter assembly, and consequently introduces a significant mass to the assembly.
As the torque converter must rotate in order to transfer torque between the engine and the transmission, any added mass to the torque converter must also be rotated during this transfer process. Due to the principle of mass moment of inertia, i.e., a measure of a solid object's resistance to changes in rotational speed about its rotational axis, it can be shown mathematically that an object having a greater mass will have a greater mass moment of inertia. The mass moment of inertia I for a torque converter can be approximated by the following formula used for a thin disk having a radius r and a mass m:
  I  =            m      ⁢                          ⁢              r        2              2  Thus it can be seen that I is directly proportional to m, and therefore as m increases, I also increases. In view of this relationship between resistance to rotation, i.e., the amount of power required by the engine to drive the torque converter, and the mass of the object rotating, the resistance to rotation may be decreased by removing mass from the torque converter.
One design which reduces the mass of the torque converter assembly is shown in the embodiment depicted in FIG. 1, i.e., a single stamped drive plate. In this design, the large mass of the welded or forged tabs is replaced by the reduced mass of the stamped plate. A secondary benefit of the single piece drive plate is the reduced cost of stamping operations verses the higher cost of forging or welding operations. Thus, the single stamped plate of FIG. 1 provides both a manufacturing cost savings as well as a mass reduction over the welded and/or forged tabs. However, the single plate design requires a significant amount of material for each stamping, i.e., a large amount of material for a drive plate and scrap material from the central region of the plate. Additionally, due to overall part size, a limited number of drive plates may be produced from a given length of sheet metal stock (see FIG. 10).
As can be derived from the variety of devices and methods directed at providing means to couple a torque converter to an engine, many means have been contemplated to accomplish the desired end, i.e., strong, reliable coupling, without sacrificing mass moment of inertia, and thus resulting in higher fuel efficiency and performance. Heretofore, tradeoffs between strength and reliability of coupling means and material mass for such means were required. Thus, there has been a longfelt need for a torque converter drive plate having high strength and reliability, while introducing a minimal mass to the overall torque converter assembly.